The present invention relates generally to fluid flow control devices. More particularly, the present invention relates to a two-step metering device for a variable capacity compressor.
Systems for conditioning air, such as, for example, HVAC systems, air conditioning systems, heat pumps, refrigerators, and freezers may include a variable capacity compressor that is designed to operate at two or more capacities. In this type of conditioning system, the operating capacity of the compressor is varied between a high capacity and a low capacity depending on the operating conditions for the system. Matching the operating capacity of the compressor with the operating conditions can improve the overall efficiency of the conditioning system.
The operating capacity of the compressor may be based on many different operating conditions for the system, including, for example, the conditioning demands of the space being conditioned. The compressor of a refrigerator, for instance, may be operated at full capacity to meet a high demand generated by the introduction of a load of relatively warm items into the cabinet of the refrigerator. The temperature of the cabinet will increase accordingly. This places a greater demand on the cooling system to return the temperature of the cabinet to an acceptable degree. In this situation, the compressor may be run at high capacity to meet the increased demand. When the temperature has been reduced to an acceptable level, the compressor may be operated at a reduced capacity to maintain the desired temperature.
The overall efficiency of a conditioning system is determined by comparing the energy put into the compressor to the amount of heat transferred from the conditioned space. As is known in the art, the greatest efficiency of a conditioning system is achieved when the compressor pressurizes an operating fluid to a predetermined pressure to take advantage of the thermodynamic characteristics of the particular operating fluid. If the compressor is operated at a reduced capacity, the compressor may either pressurize a smaller amount of fluid to the predetermined level or pressurize the same amount of fluid to a reduced level. The most efficient solution is to pressurize a smaller amount of fluid to the predetermined level to take advantage of the thermodynamic characteristics of the operating fluid.
Conditioning systems must also include an expansion valve to reduce the pressure of the operating fluid and allow the operating fluid to expand prior to transferring the heat of the refrigerant and returning to the compressor. There are known expansion valves that are capable of regulating the flow of operating fluid through a conditioning system based on the pressure and/or temperature of the operating fluid. Typically, these valves include a spring-loaded plug disposed adjacent an orifice. The pressurized operating fluid exerts a force on the plug to compress the spring and reveal the orifice. The force of the spring is selected to ensure that the operating fluid has a certain pressure before opening to reveal the orifice. However, these valves are often expensive to manufacture and are often not compatible with the varying demands of a variable capacity compressor.
In light of the foregoing there is a need for a metering device for a variable capacity compressor that is inexpensive and provides a controlled regulation of fluid flow based on the operating capacity of the compressor.